D3: persist ViewModeModel in project ext state alongside bank

Add forever-stable "view_state" key under the "reasampler" namespace.
saveToActiveProject additionally serializes the ViewModeModel;
loadFromProject restores it on every load path, defaulting on an
absent/malformed key. Model state only — no visibility apply (D4).

src/persist.cpp

@@ -163,10 +163,46 @@ void ReaSamplerSession::saveToActiveProject() {
     const std::string json = bank_.serialize();
     SetProjExtState(static_cast<ReaProject*>(proj), kProjExtNamespace,
                     kProjExtIndexKey, json.c_str());
+
+    // Additive: the Design-View model rides alongside the bank in its own key.
+    // Independent write — does not disturb the bank_index above.
+    const std::string viewJson = view_.serialize();
+    SetProjExtState(static_cast<ReaProject*>(proj), kProjExtNamespace,
+                    kProjExtViewKey, viewJson.c_str());
+
     MarkProjectDirty(static_cast<ReaProject*>(proj));
 }
 
+namespace {
+
+// Load the Design-View model from a project's view_state key, or return a fresh
+// default. An absent/empty key (older project with no view state) yields a
+// default-constructed model (Arrange + Design seeded, active = Arrange) — graceful,
+// never a crash. Malformed JSON is warned and also falls back to default, mirroring
+// the bank's malformed-index handling. The whole model round-trips: modes,
+// membership, show-both, snapshots, and active mode all ride inside the one blob.
+ViewModeModel loadViewModel(ReaProject* proj) {
+    if (!proj) return ViewModeModel{};
+    const std::string viewJson =
+        getProjExtStateString(proj, kProjExtNamespace, kProjExtViewKey);
+    if (viewJson.empty()) return ViewModeModel{};  // no stored view state -> default
+    std::optional<ViewModeModel> loaded = ViewModeModel::deserialize(viewJson);
+    if (!loaded) {
+        ShowConsoleMsg("ReaSampler: stored view state is malformed — ignoring.\n");
+        return ViewModeModel{};
+    }
+    return std::move(*loaded);
+}
+
+}  // namespace
+
 void ReaSamplerSession::loadFromProject(void* proj, const std::string& projectDir) {
+    // The view model is restored on EVERY load path (peer-symmetry with the bank
+    // reset below): switching to a project with no view state must clear stale
+    // in-memory state, not inherit the previous project's. D3 restores MODEL STATE
+    // only — no visibility/processing is applied here (that is D4).
+    view_ = loadViewModel(static_cast<ReaProject*>(proj));
+
     if (!proj) {
         bank_ = BankIndex{};
         return;